Reagent strips and films are an important analytical tool in the fields of clinical chemistry, analytical medicine and food sanitation diagnostics. In some cases, colorimetric detection schemes are used to measure the concentration of analytes on such strips and films. One type of test strip assay is a lateral flow assay. Generally, lateral flow assays are membrane-based test devices in which a sample that is suspected of containing the analyte of interest is placed at or near one end of the membrane strip. The sample is carried to the opposite end of the membrane strip by a mobile, i.e liquid phase that traverses the membrane strip by capillary action. While traversing the membrane strip, the analyte in the test sample, if any, encounters one or more reagents. The reagents can include binders for the analyte. Binders can be mobile and, therefore, flow with the sample or be immobilized on the test strip as a capture agent. Depending on the assay configuration, either the analyte binder, the analyte itself, or some other reagent in the assay system, will be captured by the immobilized capture agent and, thereby, produce a detectable signal. The signal can be generated by a label provided within the assay. The detectable signal can be measured by a reader, such as by an optical reader.
Optical analysis reader systems can include a light source, a sample, and an optical detector aligned such that the light from the light source illuminates onto the test strip and is then refracted or refracted onto the detector. The light source can include an incandescent bulb, a fluorescent tube, a light emitting diode, or the like. An example of such an optical reader is described in U.S. Pat. No. 6,124,585 (Apparatus for Measuring the Reflectance of Strips Having Non-uniform Color), issued Sep. 26, 2000, and incorporated herein by reference.
The presence and, in some cases, the concentration, of an analyte on a reagent strip sample may be determined by measuring the optical reflectance or refractance from an area of color development on the strip. Percent reflectance can be used to determine the result. The light source can be positioned to generate a light pattern on the target surface which is reflected onto an optical detector. The light source can be positioned in variety of ways and in a variety of configurations relative to the optics.
Regardless of the configuration used to illuminate the test strip onto the system optics, contamination of the optics can disrupt system measurements. Test strips are used for a variety of detection applications in a variety of matrices such as blood, urine and food. An example of such a test strip is described in U.S. Pat. No. 7,097,983 (Method for Detecting the Presence of an Analyte in a Sample), issued Aug. 29, 2006, incorporated herein by reference.
When test strips are used, for example, to detect drug residues in foods, such as milk, it is possible that food residue will remain on either or both the test strip or the test strip package when inserted into the reader. If the food residue or the like disrupts the analysis, such as by disrupting the light reflectance/refraction pattern, incorrect test results can occur. Similarly, dust or other contaminants can contaminate the optics and disrupt test results. When test results are disrupted by contaminants, readers must be either recalibrated or cleaned. The recalibration and/or cleaning processes can be time consuming and expensive.